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D J Robinson

Publications and source records attributed to D J Robinson.

At least 19 recordsLinked to original sources
PubMed2006

Laser speckle imaging of dynamic changes in flow during photodynamic therapy.

We present a study investigating the use of laser speckle imaging (LSI) for monitoring blood flow during photodynamic therapy (PDT) utilizing the therapeutic illumination radiation. The coherent nature of a laser source, often used in PDT, offers the possibility of obtaining information on the blood flow without interrupting treatment. We have found that in the rat skin-fold observation chamber, it is possible to monitor the vasculature response to PDT in individual arteries, veins and in tumour microvasculature with significantly higher spatial and temporal resolution than current methods. This illustrates the potential for LSI for monitoring PDT, in particular for vascular-localizing photosensitizers, where current non-invasive methods are difficult because of high absorption due to blood and the specific localization of photosensitizer within the vasculature. However, critical problems need to be further investigated and solved, like the influence of tissue sampling volume, changing of optical properties and movement artefacts from other vessels on the LSI signal. Until then, the real potential of LSI for monitoring blood flow remains of limited value.

Animals↗
PubMed2006

Fractionated illumination after topical application of 5-aminolevulinic acid on normal skin of hairless mice: the influence of the dark interval.

We have previously shown that light fractionation during topical aminolevulinic acid based photodynamic therapy (ALA-PDT) with a dark interval of 2h leads to a significant increase in efficacy in both pre-clinical and clinical PDT. However this fractionated illumination scheme required an extended overall treatment time. Therefore we investigated the relationship between the dark interval and PDT response with the aim of reducing the overall treatment time without reducing the efficacy. Five groups of mice were treated with ALA-PDT using a single light fraction or the two-fold illumination scheme with a dark interval of 30 min, 1, 1.5 and 2h. Protoporphyrin IX fluorescence kinetics were monitored during illumination. Visual skin response was monitored in the first seven days after PDT and assessed as PDT response. The PDT response decreases with decreasing length of the dark interval. Only the dark interval of 2h showed significantly more damage compared to all the other dark intervals investigated (P<0.05 compared to 1.5h and P<0.01 compared to 1h, 30 min and a single illumination). No relationship could be shown between the utilized PpIX fluorescence during the two-fold illumination and the PDT response. The rate of photobleaching was comparable for the first and the second light fraction and not dependent of the length of dark interval used. We conclude that in the skin of the hairless mouse the dark interval cannot be reduced below 2h without a significant reduction in PDT efficacy.

Aminolevulinic Acid↗
PubMed2005

Monitoring PDT by means of superficial reflectance spectroscopy.

Monitoring of relevant parameters during photodynamic therapy (PDT) and correlating these with treatment response is necessary to guarantee optimal and reproducible treatment outcome. In this paper we study the correlation between changes in the local tissue optical properties (absorption and scattering coefficients) during ALA-PDT and changes in PpIX fluorescence. The optical properties are measured extremely superficially by employing a single fiber for the delivery and collection of white light to and from the tissue. The measured reflectance spectrum is modeled in terms of four relevant parameters: blood saturation, relative blood volume fraction, scattering intensity and wavelength dependence of the scattering. All these parameters, except the relative blood volume fraction, are shown to correlate with the rate of photobleaching of PpIX, which in turn has previously been shown to correlate with the response of tissues to PDT. These results yield valuable insight in the behavior of these parameters during PDT and their suitability to predict PDT-response for other photosensitizers for which monitoring through photobleaching is not possible.

Aminolevulinic Acid↗
PubMed2004

Begomoviruses from mungbeans in Pakistan: epitope profiles, DNA A sequences and phylogenetic relationships.

Monoclonal antibodies raised against particles of African Cassava mosaic virus, Indian Cassava mosaic virus or Okra leaf curl virus were used to test samples collected in Pakistan from begomovirus-infected plants. Epitope profiles obtained from cucurbits resembled those previously reported for Pakistani begomoviruses. In contrast, epitope profiles obtained from legumes showed little diversity and were quite distinct from these. DNA with nucleotide sequences typical of begomovirus DNA A components was amplified from selected mungbean samples. Comparisons of the sequences of the amplified DNA with other begomovirus DNA A sequences and phylogenetic analysis revealed that the Pakistani mungbean viruses were isolates of the species Mungbean yellow mosaic India virus, which together with Mungbean yellow mosaic virus represents a distinct lineage of Old World begomoviruses.

Cucurbita↗
PubMed2003

Monitoring in situ dosimetry and protoporphyrin IX fluorescence photobleaching in the normal rat esophagus during 5-aminolevulinic acid photodynamic therapy.

Experimental therapies for Barrett's esophagus, such as 5-aminolevulinic acid (ALA)-based photodynamic therapy (PDT), aim to ablate the premalignant Barrett's epithelium. However, the reproducibility of the effects should be improved to optimize treatment. Accurate irradiation with light of a proper wavelength (633 nm), fluence and fluence rate has shown to be critical for successful ALA-PDT. Here, we have used in situ light dosimetry to adjust the fluence rate measured within the esophagus for individual animals and monitored protoporphyrin IX (PpIX) fluorescence photobleaching simultaneously. Rats were administered 200 mg kg-1 ALA (n = 14) or served as control (n = 7). Animals were irradiated with an in situ measured fluence rate of 75 mW cm-2 and a fluence of 54 J cm-2. However, this more accurate method of light dosimetry did not decrease the variation in tissue response. Large differences were also observed in the dynamics of PpIX fluorescence photobleaching in animals that received the same measured illumination parameters. We found that higher PpIX fluorescence photobleaching rates corresponded with more epithelial damage, whereas lower rates corresponded with no response. A two-phased decay in PpIX fluorescence could be identified in the response group, with a rapid initial phase followed by a slower rate of photobleaching. Non-responders did not show the rapid initial decay and had a significantly lower rate of photobleaching during the second phase of the decay (P = 0.012).

Aminolevulinic Acid↗
PubMed2001

Umbravirus-encoded proteins both stabilize heterologous viral RNA and mediate its systemic movement in some plant species.

The proteins encoded by open reading frame 3 (ORF3) of the umbraviruses pea enation mosaic virus-2 and tobacco mottle virus, like that of groundnut rosette virus, mediated the movement of viral RNA through the phloem of infected Nicotiana benthamiana or N. clevelandii plants when they were expressed from chimeric tobacco mosaic virus in place of the coat protein. However, these chimeras did not move systemically in N. tabacum. In lysates of N. benthamiana or N. tabacum protoplasts, the chimeric RNAs were more stable than was RNA of tobacco mosaic virus lacking the coat protein gene. The chimeric viruses also protected the latter in trans, suggesting that the ORF3 proteins can increase the stability of heterologous viral RNA. Umbraviral ORF3 proteins contain a conserved arginine-rich domain, and the possible roles of this motif in the functions of the proteins are discussed.

Amino Acid Sequence↗
PubMed2001

In vivo pharmacokinetics of protoporphyrin IX accumulation following intracutaneous injection of 5-aminolevulinic acid.

Photodynamic therapy with 5-aminolevulinic acid (ALA) derived protoporphyrin IX (PpIX) as photosensitizer is a promising treatment for basal cell carcinomas. Until now ALA has been administered topically as an oil-in-water cream in most investigations. The disadvantage of this administration route is insufficiënt penetration in deeper, nodular tumours. Therefore we investigated intracutaneous injection of ALA as an alternative administration route. ALA was administered in 6-fold in the normal skin of three 6-week-old female Dutch pigs by intracutaneous injection of an aqueous solution of ALA (pH 5.0) in volumes of 0.1-0.5 ml and concentrations of 0.5-2% and by topical administration of a 20% ALA cream. During 8 h fluorescence of ALA derived PpIX was measured under 405 nm excitation. For the injection the measured fluorescence was shown to be dose dependent. All injected doses of 3 mg ALA or more lead to a faster initial increase rate of PpIX synthesis and significantly greater fluorescence than that measured after topical administration of ALA. Irradiation (60 Jcm(-2) for 10 min) of the spots was performed at 3.5 h after ALA administration. After 48 and 96 h visual damage scores were evaluated and biopsies were taken for histopathological examination. After injection of 2 mg ALA or more the PDT damage after illumination was shown to be significantly greater than after topical application of 20% ALA. An injected dose of 10 mg ALA (0.5 ml of a 2% solution) resulted in significantly more tissue damage after illumination than all other injected doses.

Administration, Cutaneous↗
PubMed2001

Modeling platinum group metal complexes in aqueous solution.

We construct force fields suited for the study of three platinum group metals (PGM) as chloranions in aqueous solution from quantum chemical computations and report experimental data. Density functional theory (DFT) using the local density approximation (LDA), as well as extended basis sets that incorporate relativistic corrections for the transition metal atoms, has been used to obtain equilibrium geometries, harmonic vibrational frequencies, and atomic charges for the complexes. We found that DFT calculations of [PtCl(6)](2-).3H(2)O, [PdCl(4)](2-).2H(2)O, and [RhCl(6)](3-).3H(2)O water clusters compared well with molecular mechanics (MM) calculations using the specific force field developed here. The force field performed equally well in condensed phase simulations. A 500 ps molecular dynamics (MD) simulation of [PtCl(6)](2-) in water was used to study the structure of the solvation shell around the anion. The resulting data were compared to an experimental radial distribution function derived from X-ray diffraction experiments. We found the calculated pair correlation functions (PCF) for hexachloroplatinate to be in good agreement with experiment and were able to use the simulation results to identify and resolve two water-anion peaks in the experimental spectrum.

Journal Article↗
PubMed2000

Infective endocarditis in intravenous drug users: does HIV status alter the presenting temperature and white blood cell count?

The intent of this study was to determine if HIV seropositivity alters the maximum temperature (T(max)) and WBC count of febrile intravenous (i.v.) drug users with infective endocarditis (IE). A review of 497 charts of patients with endocarditis provided 228 eligible patient visits (46%), with 158 cases (69.3%) of IE among 126 patients (74 HIV+ and 52 HIV-). Mean T(max) for all patients with IE was 39.1 degrees C (102.4 degrees F). Mean T(max) was similar between the HIV+ (39.1 degrees C, 102.4 degrees F) and HIV- (39.2 degrees C, 102.5 degrees F) groups. There were no differences in mean T(max) among HIV+ patients with CD4 counts > 200 (39.0 degrees C, 102.3 degrees F), those with CD4 < or =200 (39.2 degrees C, 102.5 degrees F), and the HIV- group (39.2 degrees C, 102.5 degrees F). Nearly 8% of i.v. drug users with confirmed IE presented to the ED with a T(max) below 37.8 degrees C (100.0 degrees F). Mean WBC count was significantly lower in HIV+ (11.1 k/mm(3)) than in HIV- patients (15.4 k/mm(3)) and significantly lower in the group with CD4 < or =200 (8.0 k/mm(3)) than in the HIV- group. In conclusion, HIV infection was not associated with lower T(max), but it was associated with decreased WBC count in the general HIV+ group and in the group with CD4 < or =200.

Adult↗
PubMed2000

Multiple infection, recombination and genome relationships among begomovirus isolates found in cotton and other plants in Pakistan.

Begomoviruses occur in many plant species in Pakistan and are associated with an epidemic of cotton leaf curl disease that has developed since 1985. PCR analysis with primer pairs specific for each of four already sequenced types of DNA-A of cotton leaf curl virus (CLCuV-PK types a, 26, 72b and 804a), or for okra yellow vein mosaic virus (OYVMV), indicated that many individual naturally infected plants of cotton and other malvaceous species contained two or three begomovirus sequences. Similarly, sequence differences among overlapping fragments of begomovirus DNA-A, amplified from individual naturally infected plants, indicated much multiple infection in malvaceous and non-malvaceous species. Some cotton plants contained DNA-A sequences typical of begomoviruses from non-malvaceous species, and some non-malvaceous plants contained sequences typical of CLCuV-PK. Some DNA-A sequences were chimaeric; they each included elements typical of different types of CLCuV-PK, or of different malvaceous and/or non-malvaceous begomoviruses. Often an apparent recombination site occurred at the origin of replication. No complete CLCuV-PK DNA-A sequence was found in malvaceous or non-malvaceous species collected in Pakistan outside the area of the cotton leaf curl epidemic but chimaeric sequences, including a part that was typical of CLCuV-PK DNA-A, did occur there. We suggest that recombination among such pre-existing sequences was crucial for the emergence of CLCuV-PK. Recombination, following multiple infection, could also explain the network of relationships among many of the begomoviruses found in the Indian subcontinent, and their evolutionary divergence, as a group, from begomoviruses causing similar diseases in other geographical regions.

Base Sequence↗
PubMed2000

Topical 5-aminolevulinic acid-photodynamic therapy of hairless mouse skin using two-fold illumination schemes: PpIX fluorescence kinetics, photobleaching and biological effect.

Light fractionation with dark periods of the order of hours has been shown to considerably increase the efficacy of 5-aminolevulinic acid-photodynamic therapy (ALA-PDT). Recent investigations have suggested that this increase may be due to the resynthesis of protoporphyrin IX (PpIX) during the dark period following the first illumination that is then utilized in the second light fraction. We have investigated the kinetics of PpIX fluorescence and PDT-induced damage during PDT in the normal skin of the SKH1 HR hairless mouse. A single illumination (514 nm), with light fluences of 5, 10 and 50 J cm-2 was performed 4 h after the application of 20% ALA, to determine the effect of PDT on the synthesis of PpIX. Results show that the kinetics of PpIX fluorescence after illumination are dependent on the fluence delivered; the resynthesis of PpIX is progressively inhibited following fluences above 10 J cm-2. In order to determine the influence of the PpIX fluorescence intensity at the time of the second illumination on the visual skin damage, 5 + 95 and 50 + 50 J cm-2 (when significantly less PpIX fluorescence is present before the second illumination), were delivered with a dark interval of 2 h between light fractions. Each scheme was compared to illumination with 100 J cm-2 in a single fraction delivered 4 or 6 h after the application of ALA. As we have shown previously greater skin damage results when an equal light fluence is delivered in two fractions. However, significantly more damage results when 5 J cm-2 is delivered in the first light fraction. Also, delivering 5 J cm-2 at 5 mW cm-2 + 95 J cm-2 at 50 mW cm-2 results in a reduction in visual skin damage from that obtained with 5 + 95 J cm-2 at 50 mW cm-2. A similar reduction in damage is observed if 5 + 45 J cm-2 are delivered at 50 mW cm-2. PpIX photoproducts are formed during illumination and subsequently photobleached. PpIX photoproducts do not dissipate in the 2 h dark interval between illuminations.

Aminolevulinic Acid↗
PubMed1999

A plant virus-encoded protein facilitates long-distance movement of heterologous viral RNA.

Transport of plant viruses from cell to cell typically involves one or more viral proteins that supply specific cell-to-cell movement functions. Long-distance transport of viruses through the vascular system is a less well understood process with requirements different from those of cell-to-cell movement. Usually viral coat protein (CP) is required for long-distance movement, but groundnut rosette umbravirus (GRV) does not code for a CP. However, this virus moves efficiently from cell to cell and long distance. We demonstrate here that the protein encoded by ORF3 of GRV can functionally replace the CP of tobacco mosaic virus (TMV) for long-distance movement. In spite of low levels of virus RNA accumulation in infected cells, chimeric TMV with a replacement of the CP gene by GRV ORF3 was able to move rapidly through the phloem. Moreover, this chimeric virus complemented long-distance movement of another CP-deficient TMV derivative expressing the gene encoding the green fluorescent protein. Thus, the GRV ORF3-encoded protein represents a class of trans-acting long-distance movement factors that can facilitate trafficking of an unrelated viral RNA.

Journal Article↗
PubMed1999

Improvement of systemic 5-aminolevulinic acid-based photodynamic therapy in vivo using light fractionation with a 75-minute interval.

We have studied different single and fractionated illumination schemes after systemic administration of 5-aminolevulinic acid (ALA) to Improve the response of nodular tumors to ALA-mediated photodynamic therapy. Tumors transplanted on the thigh of female WAG/Rij rats were transdermally illuminated with red light (633 nm) after systemic ALA administration (200 mg/kg). The effectiveness of each treatment scheme was determined from the tumor volume doubling time. A single illumination (100 J/cm2 at 100 mW/cm2, 2.5 h after ALA administration) yielded a doubling time of 6.6+/-1.2 days. This was significantly different from the untreated control (doubling time, 1.7+/-0.1 days). The only treatment scheme that yielded a significant improvement compared to all other schemes studied was illumination at both 1 and 2.5 h after ALA administration (both 100 J/cm2 at 100 mW/cm2) and resulted in a tumor volume doubling time of 18.9+/-2.9 days. A possible mechanism to explain this phenomenon is that the protoporphyrin IX formed after administration of ALA is photodegraded by the first illumination. In the 75-min interval, new porphyrin is formed enhancing the effect of the second illumination.

Aminolevulinic Acid↗
PubMed1999

Satellite RNA is essential for encapsidation of groundnut rosette umbravirus RNA by groundnut rosette assistor luteovirus coat protein.

Groundnut rosette disease is caused by a complex of agents comprising groundnut rosette umbravirus (GRV), GRV satellite RNA (sat-RNA)groundnut rosette assistor luteovirus (GRAV). Both GRAV and GRV sat-RNA are needed for GRV to be aphid transmissible. To understand the role of GRAVGRV sat-RNA in the aphid transmission of GRV, encapsidation of GRV genomicsatellite RNAs has been studied using transgenic Nicotiana benthamiana plants expressing GRAV coat protein (CP). GRAV CP expressed from a transgene was shown to package GRV genomicsatellite RNAs efficiently, giving a high yield of transcapsidated virus particles. GRV sat-RNA was absolutely essential for this process. GRV genomic RNA was not encapsidated by GRAV CP in the absence of the sat-RNA. Using different mutants of GRV sat-RNA, it was found that some property of full-length satellite RNA molecules, such as size or specific conformation rather than potential open reading frames, was required for the production of virus particles. A correlation between the ability of sat-RNA to stimulate encapsidation of GRV RNA by GRAV CPits capacity to promote aphid transmission of GRV was observed.

Animals↗
PubMed1999

Erythroplasia of Queyrat treated by topical aminolaevulinic acid photodynamic therapy.

Erythroplasia of Queyrat (EQ) is an intraepithelial carcinoma in situ affecting the mucosal surfaces of the penis, with a significant risk of invasion and metastasis. Treatment is often difficult and is associated with significant recurrence rates. Topical 5-aminolaevulinic acid (ALA) photodynamic therapy (PDT) combines a photosensitizer precursor and visible light to produce a photodynamic effect. It has been used successfully to treat benign, premalignant and malignant skin diseases. We present four patients with EQ who have been treated by topical ALA PDT. Of two patients with limited disease one has achieved a long-term complete response (36 months) and the other developed a recurrence at 18 months after a complete response. Two further patients with more extensive disease achieved a significant improvement, allowing easier treatment by laser vaporization. Although topical ALA PDT offers the advantages of tumour specificity, preservation of function and a good cosmetic result, more extensive EQ appears less responsive to this new therapeutic modality using current treatment parameters.

Administration, Topical↗
PubMed1999

Improved response of plaque psoriasis after multiple treatments with topical 5-aminolaevulinic acid photodynamic therapy.

We investigated the clinical response of 10 patients with plaque psoriasis to multiple treatments with photodynamic therapy, using topical application of 5-aminolaevulinic acid followed by exposure to broad-band visible radiation. Treatment was performed up to 3 times per week, with a maximum of 12 treatments, using a light dose of 8 Jcm(-2) delivered at a dose-rate of 15 mW cm(-2). Eight patients showed a clinical response. Out of 19 treated sites, 4 cleared, 10 responded but did not clear and 5 showed no improvement. Of the 4 sites that cleared only 1 did so fully, after 7 treatments, 45 days after the start of therapy. Of the 10 sites that responded partially, the greatest reduction in scale, erythema and induration index occurred after a minimum of 3 and a maximum of 8 treatments. The intensity of 5-aminolaevulinic acid-induced protoporphyrin IX fluorescence, recorded prior to the first treatment, varied between sites on the same patient as well as between patients. There was also a variation in fluorescence intensity recorded from the same site immediately prior to subsequent treatments, although the pretreatment levels generally decreased as the study progressed and then increased as psoriasis relapsed. Biopsies confirmed that fluorescence was localized throughout the epidermis and stratum corneum, but the level was not consistent between sections taken within the same biopsy. We also observed fluorescence at sites distant from the ones that received 5-aminolaevulinic acid, which was not present prior to the start of the treatment programme, but found no evidence of elevated levels of plasma porphyrins. The level of discomfort associated with this therapy increased with increasing values of the calculated photodynamic dose, defined as the product of the initial photosensitizer concentration and the percentage reduction in fluorescence following irradiation. Therefore, although clinical efficacy improved with multiple treatments, unpredictable response and patient discomfort make ALA-PDT unsuitable for the treatment of psoriasis.

Administration, Topical↗